I will agree with the Abercrombie suggestion. I think there's alot of ambivalence and darkness there. I only read the first book of the triology and overall it didn't ring my bell, but in terms of what you're looking for it sounds like a good fit.
I quite enjoy Glen Krisch when it comes to darkness in general. In particular - Where Darkness Dwells, but The Nightmare Within also sounds like it could hit some of your sweet spots.
I recently read The Tube Riders by Chris Ward and I thought that was pretty dark and very enjoyable as long as you don't mind most of the protagonists being children/teenagers.
I would also put 1984 by George Orwell and The Handmaid's Tale by Margaret Atwood in the list.